Re: [PATCH 00/14] sched: Support shared runqueue locking

Andrea Righi
2025-09-11T14:51:58Z

On Thu, Sep 11, 2025 at 11:58:45AM +0200, Peter Zijlstra wrote:
> On Wed, Sep 10, 2025 at 08:35:55PM +0200, Peter Zijlstra wrote:
>
> > I'll go untangle it, but probably something for tomorrow, I'm bound to
> > make a mess of it now :-)
>
> Best I could come up with is something like this. I tried a few other
> approaches, but they all turned into a bigger mess.
>
> Let me go try and run this.

With this one it's complaining about lockdep_assert_held(p->srq_lock):

[ 19.055730] WARNING: CPU: 2 PID: 368 at kernel/sched/core.c:10840 sched_change_begin+0x2ac/0x3e0
...
[ 19.056468] RIP: 0010:sched_change_begin+0x2ac/0x3e0
...
[ 19.057217] RSP: 0018:ffffa9f7805bbde8 EFLAGS: 00010046
[ 19.057359] RAX: 0000000000000000 RBX: ffff97ae04880000 RCX: 0000000000000001
[ 19.057464] RDX: 0000000000000046 RSI: ffff97ae01715518 RDI: ffff97ae027f0b68
[ 19.057568] RBP: 0000000000000082 R08: 0000000000000001 R09: 0000000000000001
[ 19.057706] R10: 0000000000000001 R11: 0000000000000001 R12: ffff97ae3bdbcc80
[ 19.057833] R13: ffff97ae93c48000 R14: ffff97ae3b717f20 R15: 0000000000000000
[ 19.057973] FS: 00007f18999edb00(0000) GS:ffff97ae93c48000(0000) knlGS:0000000000000000
[ 19.058112] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 19.058223] CR2: 000055e1e6b0246c CR3: 0000000102ce8000 CR4: 0000000000750ef0
[ 19.058460] PKRU: 55555554
[ 19.058561] Call Trace:
[ 19.058604] <TASK>
[ 19.058675] __set_cpus_allowed_ptr_locked+0x17c/0x230
[ 19.058769] __set_cpus_allowed_ptr+0x64/0xa0
[ 19.058853] __sched_setaffinity+0x72/0x100
[ 19.058920] sched_setaffinity+0x261/0x2f0
[ 19.058985] __x64_sys_sched_setaffinity+0x50/0x80
[ 19.059084] do_syscall_64+0xbb/0x370
[ 19.059158] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 19.059236] RIP: 0033:0x7f189a3bd25b

Thanks,
-Andrea

>
> ---
> kernel/sched/core.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2481,11 +2481,11 @@ static inline bool is_cpu_allowed(struct
> * Returns (locked) new rq. Old rq's lock is released.
> */
> static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
> - struct task_struct *p, int new_cpu)
> + struct task_struct *p, int new_cpu, int flags)
> {
> lockdep_assert_rq_held(rq);
>
> - deactivate_task(rq, p, DEQUEUE_NOCLOCK);
> + deactivate_task(rq, p, flags | DEQUEUE_NOCLOCK);
> set_task_cpu(p, new_cpu);
> rq_unlock(rq, rf);
>
> @@ -2493,7 +2493,7 @@ static struct rq *move_queued_task(struc
>
> rq_lock(rq, rf);
> WARN_ON_ONCE(task_cpu(p) != new_cpu);
> - activate_task(rq, p, 0);
> + activate_task(rq, p, flags);
> wakeup_preempt(rq, p, 0);
>
> return rq;
> @@ -2533,7 +2533,7 @@ static struct rq *__migrate_task(struct
> if (!is_cpu_allowed(p, dest_cpu))
> return rq;
>
> - rq = move_queued_task(rq, rf, p, dest_cpu);
> + rq = move_queued_task(rq, rf, p, dest_cpu, 0);
>
> return rq;
> }
> @@ -3007,7 +3007,7 @@ static int affine_move_task(struct rq *r
>
> if (!is_migration_disabled(p)) {
> if (task_on_rq_queued(p))
> - rq = move_queued_task(rq, rf, p, dest_cpu);
> + rq = move_queued_task(rq, rf, p, dest_cpu, DEQUEUE_LOCKED);
>
> if (!pending->stop_pending) {
> p->migration_pending = NULL;